The invention relates, in general, to coal gasification and, more particularly, to a method and apparatus for cooling and separating chlorides and fluorides from ammonical gas particularly from coal carbonization or gasification gas.
Aside from the acid components-CO.sub.2, H.sub.2 S, HCN, the gas obtained during coal carbonization or gasification also contains HCl, HF and NH.sub.3 in varying concentrations, depending upon the characteristics of the charged coal and the operating conditions.
In treating the gas for use as fuel or synthesis gas, the acid components are substantially removed in physical or chemical wet scrubbing processes. Advance separation of chlorides and fluorides is a prerequisite for the application of wet scrubbing to remove sulfur or carbon dioxide in order to keep the chloride and fluoride concentration in the scrubbing circuit at a tolerable level, without the necessity of removing the wash liquor. The removal of wash liquor must be avoided since, irrespective of the costs of resupplying with fresh liquor, disposal of the removed amounts is very expensive if environmental protection is to to be observed. Wet processes for removing sulfur and carbon dioxide, furthermore, require a preliminary cooling of the gas to a temperature ranging from 30.degree. C. to 100.degree. C. prior to its introduction into the scrubber.
With an indirect gas cooling by means of heat exchangers, gaseous NH.sub.3 and HCl will form solid NH.sub.4 Cl which deposits on the surfaces of the cooler. This requires periodic solid removal. Therefore, a continuous operation is not possible with such heat exchangers. In addition, depending on the vapor pressure of NH.sub.4 Cl (p NH.sub.3 +p HCL), chlorides are only partly removed. Therefore, to obtain the required small residual amounts of chlorides and fluorides, wet scrubbers or wet electrofilters are needed for further separation. This results in increased equipment and operating costs.
Attempts have been made to directly cool and separate the gas in the scrubbers by water evaporation and, at the same time, to separate the chlorides and fluorides. Fresh water is supplied for this purpose into the washing circuit. The NH.sub.3 contained in the gas combines with the acid gas components, preferably with HCl and HF. However, with direct cooling of the gases by water evaporation. NH.sub.4 Cl and NH.sub.4 F aerosols form from a part of the NH.sub.3, HCl, and HF and the evaporated drops of the solution, and a considerable amount of energy is required for further separation.